I am trying to set up an email server in a vmware virtual machine. I want traffic to this machine to pass through pfSense. So I have a virtual machine that contains the email server at 172.16.150.3. This is on the host only network. I can access it directly, but when I try to reach it through 10.99.99.6, I can not. The packets are being filtered.

If you are looking for help on the forum because you have a problem:
provide as much information as possible.
(log-outputs, screenshots of config/rules, etc.)
Often a Diagram (ASCII ART ?) can help more than pages of descriptions how your network is set up.

You run a mailserver on 172.16.150.3 and you want to be able to connect to 10.99.99.6 and access this mailserver.
For this to work you need to forward the ports on which your server is reachable.
just a firewall rule is not enough.
Create forwardings under Firewall–>NAT